1. Field of the Invention
The present invention relates to a cooling apparatus, particularly an adsorption type cooling apparatus that is applicable to an air-conditioning system of automobiles, vessels, residences, or shipping containers for food products or medical products that require refrigeration.
2. Description of the Prior Art
Prior known cooling apparatuses for air-conditioning or refrigeration include a well-known conventional heat pump system and, more recently, an adsorption system that uses adsorbents such as zeolite.
The prior technology is exemplified by what is described in Japanese Laid-Open Patent Application 61-139098, filed Jun. 14, 1986, Laid-Open No. 62-5060, laid-open Jan. 12, 1987, priority being claimed on West Germany (DE) Patent Application P3521484.8, filed Jun. 14, 1985.
The present applicant has disclosed improved adsorption-type cooling systems in copending U.S. applications, Ser. Nos. 08/066,984 filed May 25, 1993 and 08/085,323 filed Jun. 29, 1993.
FIGS. 6a and 6b illustrate a basic principle of a prior known single-adsorber type adsorption cooling system. In FIG. 6a, an adsorber 1 is connected with a cooling vessel 2 by a tubular passage 4 having a shutoff valve 3. The adsorber 1 houses adsorbent la such as zeolite, and a heat exchange pipe 5 that is in contact with the adsorbent 1a. The cooling vessel 2 contains water as an adsorption medium (adsorbate) which is in thermal contact with a cooling pipe 6. The air that is to be cooled is circulated through the cooling pipe 6. The adsorber 1, the cooling vessel 2 and the tubular passage 4 constitute a closed system which is evacuated of air. A condenser 7 for exchanging heat with the ambient air is provided on the tubular passage 4 near the cooling vessel 2.
With this cooling system, when the valve 3 is opened, the water inside the cooling vessel 2 evaporates into water vapor and shifts through the tubular passage 4, in the direction shown by the arrow, into the adsorber 1 to be adsorbed by the adsorbent la by its adsorption action. Because of this, when the water in the cooling vessel 2 evaporates, the latent heat of evaporation is consumed in the cooling vessel 2, so that the temperature in the cooling vessel 2 declines so as to cool the air inside the cooling pipe 6. This operation is called an adsorption process.
Next, an explanation will be made on the operation whereby the water adsorbed by the adsorbent la is returned to the cooling vessel 2.
Referring to FIG. 6b, a high temperature gas from an external heat source is provided through the heat exchange pipe 5 to heat the adsorbent la and thereby desorb and separate the water adsorbed therein. Then, the separated water in a state of vapor is driven through the tubular passage 4, in the direction shown by the arrow, to the condenser 7, where the water vapor turns into liquid water and is recovered in the cooling vessel 2. This operation is called a desorption process.
The adsorption here means a state where the water molecules are retained among the molecules of the adsorbent. Reversely, in the desorption action, the water molecules are desorbed and separated from the molecules of the adsorbent as the adsorbent is heated.
However, the single-adsorber type adsorption cooling system described above is incapable of continuous cooling because the adsorption process and the desorption process must be done alternately in the same system. With this in mind, a dual-adsorber type adsorption cooling system as shown in FIG. 7 has been proposed.
In FIG. 7, two adsorbers 8, 9 are individually connected to a single cooling vessel 14 by tubes 12, 13, which respectively have shutoff valves 10, 11. The water in the cooling vessel 14 is thermally contacted by a cooling pipe 15 in the same manner as in the case of the single-adsorber type adsorption cooling system described above. Adsorbents 8a, 9a in the adsorbers 8, 9 are also in thermal contact with heat exchange pipes 16, 17, respectively, and condensers 18, 19 are provided on the tubes 12, 13, respectively.
With this cooling system, while the adsorption process is performed at one adsorber, at, for example, the adsorber 8, the desorption process is simultaneously performed at the other adsorber 9. Then, the two adsorbers 8, 9 carry out a switching operation whereby they work in reverse when their respective processes have been completed. Since the adsorber 9 is at high temperature when the desorption operation has been completed, low or ambient temperature air is provided through the heat exchange pipe 17 to cool the adsorbent 9a. Continuous cooling in the cooling vessel 14 is thus made possible by periodically repeating such operation.